1. Field of the Invention
This invention is in the field of fluorine chemistry, and more particularly in the field of direct fluorination.
2. Description of the Prior Art
Fluorinated compositions are known to possess many outstanding properties. The range of these properties is indicated by the broad range of utilities for fluorinated compositions, which includes lubricants, heat transfer media, solvents, plasticisers, waxes, sealing liquids, refrigerants, surface active agents, oil and water repelling agents, inert solvents, diluents, monomers for preparing valuable fluoropolymers, and many others. Because of their value, extensive research has been devoted to preparing fluorinated products.
Fluorination processes present many problems, however. Whereas many compositions can be directly chlorinated or brominated, it has been recognized that fluorine is dissimilar to these halogens in regard to direct halogenation. See McBee et al., U.S. Pat. No. 2,533,132 and U.S. Pat. No. 2,614,129. In fact, even though direct fluorination of compositions with fluorine gas is a highly desirable process, prior attempts to use direct fluorination have usually produced low to mediocre yields. Additionally, the yields decrease as the molecular complexity of the reactants becomes greater.
Direct fluorination reactions involving elemental fluorine are characterized by quick evolution of large quantities of heat, ignition and flaming which promote product decomposition, often with explosive violence. In fact, it has been stated that "The fluorination process using elemental fluorine is one in which complete combustion of the hydrocarbon to carbon tetrafluoride and hydrogen fluoride is normally competing at a substantial rate with the desired fluorination." See Benning, U.S. Pat. No. 2,505,877. Thus, inability to control direct fluorination reactions to produce high yields of the desired fluorinated reactant without concomittant fragmentation of the desired product has prevented direct fluorination from becoming a widely accepted method of fluorination.
Because of the problems associated with previous attempts to use direct fluorination processes, a very diversified art has been developed to circumvent or obviate these problems utilizing inorganic, metallic fluorides, hydrogen fluoride, or electrolytic cells where no free fluorine is produced. The patent literature is replete with descriptions of such processes. A sampling includes: fluidized bed reaction employing metal fluorides such as cobalt trifluoride (McCleary, U.S. Pat. No. 2,759,026); syntheses of liquid fluorohalocarbons by reacting elemental fluorine with a fluidized mass of finely divided carbon particles in a reaction zone at 500.degree.-800.degree. F. and in the presence of chlorine or bromine (Mantell et al., U.S. Pat. No. 2,774,797); catalytic reaction of organic perchlorofluorocarbons with elemental fluorine or chlorine trifluoride in the presence of aluminum trifluoride catalysts (Tyczkowski et al., U.S. Pat. No. 2,831,035); contacting vapor phase hydrocarbons which contain halogens other than fluorine with chlorine trifluoride or chlorine monofluoride (Muray, U.S. Pat. No. 3,099,695); contacting gaseous fluorine in the presence of alkali metal fluoride catalysts such as lithium fluoride at temperatures from -100.degree. C. to 200.degree. C. (Siegart, U.S. Pat. No. 3,480,667); and, combination electrochemical and chemical fluorination together with proper fractionation steps to fluorinate compounds containing chlorine or bromine using hydrogen fluoride, elemental fluorine or chlorine trifluoride (Fox, U.S. Pat. No. 3,709,800). It should be understood that the preceding fluorination processes are merely selected randomly from the patent literature, and are not intended to be inclusive of the general state of the art.
Recently, a new process for direct fluorination, known as the La-Mar process, has been used to fluorinate hydrogen-containing organic, organometallic and inorganic materials including aromatic ring systems. In this process, the hydrogen-containing material is placed in an enclosed chamber and an inert atmosphere such as nitrogen is introduced. Fluorine gas or an inorganic fluoride is introduced into the inert atmosphere in a very low initial concentration such as not to exceed about 6% at the end of 30 minutes. The temperature is maintained at a uniform low temperature so as to avoid uncontrolled fluorination. The La-Mar direct fluorination process is further disclosed in the following references: Lagow, R. J. and Margrave, J. L.; "Direct Fluorination of Organic and Inorganic Substances," Proc. Natl. Acad. Sci., 67; 4, 8A (1970); Lagow, R. J. and Margrave, J. L.; "The Reaction of Polynuclear Hydrocarbons with Elemental Fluorine," J. Am. Chem. Soc. (submitted); Lagow, R. J. and Margrave, J. L.; Chem. Eng. News, 48; 40 (Jan. 12, 1970); and U.S. Patent Applications Ser. No. 718,128 (1968), Ser. No. 133,804 (1971), Ser. No. 133,803 (1971), and Ser. No. 133,865 (1971).
Although the La-Mar direct fluorination process has extended the application of direct fluorination, this process still has inherent limitations. For example, it is not suitable for fluorinating many gases and liquids. Additionally, hydrocarbons containing oxygen are difficult or impossible to fluorinate in a controllable manner by the La-Mar process. One reason for this is, of course, that oxygen-containing compounds tend to fragment during fluorination resulting in the formation of free radicals which tend to initiate polymerization of reactants into polymers. It will be recognized, of course, that many valuable organic compounds contain functional groups including oxygen, such as ethers, esters, ketones, alcohols, carboxylic acids, etc. Thus, there still exists a need for a new direct fluorination apparatus and process which would provide sufficient flexibility to make it applicable to a wide range of reactants to be fluorinated, including oxygen-containing compounds.